Heat pump systems for residential use

ABSTRACT

An air conditioning system of the air cycle heat pump type for selectively heating and cooling a residence or similar space environment. In one embodiment, a combustor and associated Brayton cycle turbine provide the primary drive to a compressor constituting the heat pump. In a second embodiment, the Brayton turbine is replaced by an electric motor coupled to drive the compressor shaft. An auxiliary turbine is also coupled to the drive shaft to provide auxiliary drive derived from the operation of a portion of the system at sub-atmospheric pressure. In this portion, during the cooling mode, water is evaporated into the system to further assist in cooling by removing the latent heat of vaporization.

This is a division of application Ser. No. 172,631, filed July 25, 1980,now U.S. Pat. No. 4,347,714.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to systems for space heating and cooling and,more particularly, to such systems particularly adapted to provideimproved efficiency for residential use.

2. Description of the Prior Art

Heat pumps have long been used for efficiently transferring heat fromone medium to another, thus permitting the heating or cooling of a givenspace with the heat being transferred from some readily available medium(ambient air, water in an adjacent lake or well, a body of rocks orsalt, or the like) for heating, and being delivered to the medium (oftenthe same body of water, etc.) for cooling.

For example, the Carleton patent, U.S. Pat. No. 3,135,318 describes aheat pump system using a turbo-compressor which provides power and wasteheat to a standard vapor cycle refrigeration system. Two turbines areemployed in the system, one driving the turbo-compressor and a secondturbine driving a recirculating air fan and the refrigerant compressor.

The Miller patent, U.S. Pat. No. 3,822,561, describes a self-contained,portable air cooling unit comprising a refrigeration circuit, a thermalreservoir consisting of an ice bank in a flexible tank, and a heatexchanger for transferring heat between the air in the space to becooled and chilled water circulated from the ice bank and reservoir.Means are provided to selectively and alternatively operate therefrigeration circuit and the circulating system to heat or to cool thespace as desired.

The Lodge patent, U.S. Pat. No. 3,407,620 describes a system for heatingand cooling using a recirculating water loop. Heating is supplied by astandard heater using combustible fuel, and cooling is provided by acooling tower. Although the patent represents the system as a heat pump,it is not a heat pump by the usual thermodynamic definition.

The La Fleur patent, U.S. Pat. No. 3,355,903, describes a closedreverse-Brayton-cycle refrigeration system to provide refrigeration forair liquefaction. Repetitive stages of compression and cooling areemployed.

A heat-actuated space conditioning system utilizing a Brayton engine isdescribed in an article entitled "Light Commercial Brayton/Rankine SpaceConditioning System" by David Friedman, beginning at page 172 of theAugust, 1977 Proceedings of the 12th IECEC (Intersociety EnergyConversion Engineering Conference). This article describes a Braytoncycle system utilizing a combustor driving a turbo-compressor, thelatter being magnetically coupled to a second compressor in anassociated Rankine cycle system.

Such systems as are known may provide improved efficiency over thestandard air conditioning system including a furnace for heating and arefrigeration type air conditioner for cooling, but the cost of such aheat pump system is generally substantially greater because of theincreased complexity. However, with the recent substantial increases inthe cost of fuel, it becomes more worthwhile, indeed essential, todevelop systems of improved efficiency.

The present invention is directed to the provision of a simplified heatpump system of improved efficiency for selectively heating or cooling aresidential space in a temperate zone region where extreme low and hightemperatures are seldom encountered.

SUMMARY OF THE INVENTION

In brief, arrangements in accordance with the present inventionincorporate a turbo-compressor, a pair of heat exchangers, and suitablecontrol valves in a basic reverse-Brayton-cycle heat pump adapted forresidential use. The control valves may be adjusted to cause the systemto operate in either a heating or a cooling mode. High efficiency isachieved by, among others, regeneratively heat exchanging with inletambient air and expanding the ambient air through a turbine prior toexhaust. In addition, other waste heat from the system is used inheating the conditioned space.

In one arrangement in accordance with the invention, a recuperatedBrayton cycle engine is mounted on a common shaft with theaforementioned turbo-compressor to provide the primary drive. In thisembodiment, the Brayton engine uses a heat source in the form of acombustor and heat exchanger adapted to burn natural gas. An additionalsink heat exchanger is provided and arranged, in the heating mode, toadd the waste heat from the drive portion of the system to the air forthe residential conditioned space.

In a second embodiment, the primary source of driving power is providedby an electric motor coupled to the shaft of the turbo-compressor. Inthe heating mode, air is directed through a heat exchanger coupled tothe motor so that motor heat is added to the air supplied to the loadheat exchanger for the conditioned space.

In both embodiments, the Brayton cycle portion of the system is operatedat sub-atmospheric pressure. In the cooling mode, advantage is taken ofthis condition to provide additional cooling through the injection ofwater spray into the low pressure side of the load heat exchanger.Evaporation of water is enhanced because of the sub-atmospheric pressurelevel, and additional cooling is effected through the removal of thelatent heat of vaporization.

Because the working fluid for both the Brayton cycle engine and theBrayton conditioning cycle is air, the two systems can share a commoncompressor.

BRIEF DESCRIPTION OF THE DRAWING

A better understanding of the present invention may be had from aconsideration of the following detailed description, taken inconjunction with the accompanying drawing in which:

FIG. 1 is a schematic diagram illustrating one particular arrangement ofa heat driven heat pump in accordance with the invention, shown in theheating mode;

FIG. 2 is a schematic diagram illustrating the arrangement of FIG. 1 foroperation in the cooling mode;

FIG. 3 is a schematic diagram showing a variation of the system of FIGS.1 and 2;

FIGS. 4A and 4B are schematics illustrating another arrangement of theinvention in the heating and cooling modes, respectively;

FIG. 5 is a schematic diagram of an arrangement of an electricallydriven heat pump in accordance with the invention, shown for operationin the heating mode; and

FIG. 6 is a schematic diagram of the arrangement of FIG. 5, shown foroperation in the cooling mode.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2 represent schematically a heat-driven, air cycle heat pumpsystem 10 in accordance with the invention, particularly adapted forresidential use. In these figures, the system 10 is shown comprising aload heat exchanger 12 connected to ducting 14 through which air to beheated or cooled is driven by a fan 16.

The air cycle, or Brayton cycle, portion of the system 10 comprises aturbo-compressor 18 having a turbine 20 and compressor 22 interconnectedwith a regenerative heat exchanger 24 for ambient air and the load heatexchanger 12 via heat/cool control valves 26, 28.

The drive portion of the system 10 is shown comprising a Brayton cycleturbine 30 coupled on a common shaft 32 with the turbo-compressor 18 andconnected to receive heated air from a combustor/heat exchanger 34 fedby natural gas. The exhaust of the turbine 30 is fed to a secondregenerative heat exchanger 36 from whence it passes to a sink heatexchanger 38 connected in an air duct 40 having a fan 42. The duct 40 isconnected via ducting 44 to the main air duct 14 and by ducting 46 tooutlets for ambient air. Dampers 48 are provided to select the path forair flowing through the duct 40.

As shown in FIG. 1, the valves 26, 28 and the dampers 48 are positionedfor operation of the system in the heating mode. In this mode, coldambient air ducted from outside the house is first heated in theregenerative heat exchanger 24 to near the temperature of the heatedspace and then is directed through valve 28 to the common compressor 22.This air is mixed with air from the sink heat exchanger 38 andcompressed by the compressor 22. The temperature of the compressed airis raised well above that required for the heated space and a portion isducted through valve 26 to the load heat exchanger 12 where it providesthe heat for the recirculated air. This air then returns through theregenerative heat exchanger 24, providing the source of heat for theambient air, and thus is cooled to near ambient temperature. Next itpasses through the valve 28 to the turbine 20 where it is expanded to atemperature well below ambient and is exhausted to ambient through thevalve 26. This expansion process in the turbine 20 provides a portion ofthe energy needed to drive the compressor 22. The remaining energy isprovided by the Brayton turbine 30.

Air from the sink heat exchanger 38 is mixed with the preheated ambientair at the inlet of the compressor 22 where it is compressed and aportion is directed through the recuperator 36 and combustor/heatexchanger 34, where the temperature is increased to approximately 1500degrees F. The air is then expanded across the turbine 30 to provide theremaining energy to drive the compressor 22. The air leaving the turbine30 then passes through the recuperator 36 and the sink heat exchanger38. A portion of the recirculated air from the duct 14 passes via ducts44 and 40 through the sink heat exchanger 38 to add the waste heat fromthe Brayton engine drive portion of the system 10 to the recirculatedair as additional heating.

FIG. 2 shows the system of FIG. 1 for operation in the cooling mode. Thevarious components of the system are shown with the same referencenumerals and are the same as depicted in FIG. 1 with the exception thatthe valves 26, 28 and the dampers 48 are changed to the cool positions,and a water spray system (omitted from FIG. 1 for simplicity) is shown.The water spray system comprises a spray unit 50 at the inlet of thecool side of the heat exchanger 12 and water recirculation is providedby a sump 52 and pump 54 through recirculating line 56. A water make-upline 57 is also provided.

In the operation of the arrangement of FIG. 2 for cooling residentialspace air, warm ambient air is first cooled in the regenerative heatexchanger 24 to near the temperature of the conditioned space and thenis directed to the turbine 20 where it is expanded to sub-atmosphericpressure. The temperature of the ambient air is thus decreased wellbelow the temperature of the conditioned space. The expansion energyprovides a portion of the energy required to drive the compressor 22.The remainder of the energy will be provided by the Brayton turbine 30,as previously described.

After leaving the turbine 20, the cooled air is directed through theheat exchanger 12 to provide the cooling for the conditioned space. Theair is then directed through the regenerative heat exchanger 24 and thevalve 28 to the inlet of the compressor 22 where it is mixed with airfrom the sink heat exchanger 38. Waste heat removed by the sink heatexchanger 38 is ducted to atmosphere via the ducts 40, 46, as propelledby the fan 42. Air from the inlet of the compressor 22 is compressedback to ambient pressure and the portion not returned to the driveportion of the system is exhausted to atmosphere through the valve 26.

In the cooling mode, the inlet of the compressor 22 is sub-atmospheric,and thus the Brayton cycle engine must operate in the closed mode.Starting at the inlet of the compressor 22, the air is compressed anddirected through the recuperator 36 and combustor/heat exchanger 34where the temperature is increased to about 1500 degrees F. The air isthen expanded across the turbine 30 to provide the necessary energy todrive the compressor 22. The hot turbine discharge air is now directedthrough the recuperator 36 and the sink heat exchanger 38.

The water evaporation from the spray unit 50 within the load heatexchanger 12 provides a significant additional cooling in the system.The chamber is flooded for maximum evaporation; excess water is drawnoff in the sump 52. Any condensation from ambient air may also be usedin the spray system.

In a variant of the arrangements of FIG. 1 and 2, shown schematically inFIG. 3, the waste heat from the recuperator 36 is introduced to therecirculated air duct in a somewhat different fashion. In FIG. 3, inwhich like elements have been given like reference numerals, theauxiliary heat ducting 40, 44 has been replaced by ducts 41, 43 and 45.Ducts 43 and 41 interconnect to the inlet of the compressor 22 via avalve 49 at the outlet of the sink heat exchanger 38. Duct 45 extendsfrom the inlet side of the heat exchanger 38 (recuperator 36 outlet) tothe downstream side of the air circulation duct 14 to transmit air fromthe recuperator 36 directly into the air circulation return. A valve 37is provided in the duct 45 to block backflow into the sub-atmosphericcycle during operation in the cooling mode.

In the heating mode operation as shown in FIG. 3, auxiliary air from therecirculation duct 14 is taken off upstream of load heat exchanger 12and passes via ducts 43, 41 and the valve 49 directly to the inlet sideof the compressor 22. Valve 49 blocks the outlet of the sink heatexchanger 38 so that no air passes through the exchanger 38. Instead,the air from the recuperator 36, which is still at an elevatedtemperature and possesses substantial heat, passes to the aircirculation return 14 by way of the duct 45. In the heating mode, thisair provides about 60% of the heating capacity for the system. Exceptfor this variation, the operation of the system of FIG. 3 is the same aspreviously described for FIG. 1 in the heating mode. In the coolingmode, the valve 49 is turned so as to block air flow through the ducts41 and 43 and to direct air from the sink heat exchanger 38 to thecompressor 22. In the cooling mode, no air flows through the duct 45.

Still another variation of the heat-driven air-cycle heat pump of thepresent invention is illustrated schematically in FIGS. 4A and 4B. Thisis essentially like the arrangement of FIG. 3 except that a pair ofturbo-compressors are provided in place of the single three-wheel turbomachine of FIG. 3. In the schematic diagrams of FIGS. 4A and 4B, thetransfer valves have been omitted for the sake of simplicity.

FIGS. 4A and 4B represent the operation of the dual turbo-compressorsystem in the heating and cooling modes, respectively. As depicted, thesystem includes a pair of turbo-compressors 60, 64. The unit 64 is inthe Brayton cycle heat pump portion of the system which is drivenpneumatically by the Brayton power cycle portion of the system,comprising the turbo-compressor 60. As a further modification, ducting68, including fan 69, is provided to introduce ambient air into therecirculation air for the house after the ambient air passes through theregenerator 24.

In this arrangement, both the power and conditioning cycle compressors62, 66 take in house air as the cycle working fluid. The air iscompressed with a consequent increase in temperature, and about 40% ofthe power cycle air from compressor 62 is added to the conditioningcycle at the outlet of the compressor 66. This high pressure aireventually expands through the conditioning cycle turbine 65--afterpassing through the load heat exchanger 12 and the regenerator 24--toprovide the power that drives the conditioning cycle turbomachine 64. Inthis process, the conditioning cycle air is cooled to near house airtemperature by the recycled house air in the load heat exchanger 12. Thehouse air in turn gains heat and is ducted back to the house at anelevated temperature to provide heating. In passing through theregenerator 24, the cycle air is cooled by ambient air coming into thehouse, which in turn is heated to approximately the temperature of thehouse and is mixed with the house return air via duct 68. This fresh airreplaced the conditioned cycle air which is leaving the house andpreserves air flow balance within the house.

The cycle air at the conditioned air turbine 65 expands to ambientpressure and is released to atmosphere. The power generated by theturbine 65 drives the compressor 66.

After the approximately 40% of the power cycle air is bled off to theoutlet of the compressor 66, as described above, the remaining 60%passes through the recuperator 36 and combustion heat exchanger 34 whereit is heated to its maximum temperature. This air is then expandedthrough the power cycle turbine 61, generating the power to drive thepower cycle compressor 62. This air is still hot and passes through tothe other side of the recuperator 36 and is returned to the house viathe auxiliary return duct 68A which joins the main return duct 14. Thesink heat exchanger 38 is not utilized in the system when in the heatingmode corresponding to FIG. 4A.

When the two transfer valves (see FIG. 1) are rotated to switch fromheating to cooling, thus developing the system configuration as shown inFIG. 4B, the conditioning cycle also shifts from pressurized operationto sub-atmospheric. A comparison of FIGS. 4A and 4B indicates that thepower cycle air is routed through the power cycle turbomachinery asbefore, but the conditioning cycle air now goes through the turbine 65first, instead of the compressor 66. The conditioning cycle air is takenfrom the house via duct 67 and expanded through the turbine 65 tosub-atmospheric pressure where the work of expansion causes a drop inair temperature. Next, water is sprayed into the lower pressure air by aspray head 50 at the input to the load heat exchanger 12. This waterevaporates to remove the heat of vaporization from the house air in theload heat exchanger 12. Because of the low sub-atmospheric pressure, theair will hold more water than normal, and the evaporative coolingcapability of the cycle air is increased. The recirculated house air inturn is cooled by the cycle air, and any excess moisture condenses onthe downstream side of the load heat exchanger 12. This moisture, alongwith a minor amount of makeup water, is used for the water spray supply(not shown). The regenerator 24 then cools the ambient air introducedinto the house to replace the air expelled from the house by the cycle.Any condensation from the ambient air is also used for the spray system69.

The low pressure air is next pumped up to ambient levels by the twocompressors 62, 66. The power generated by the conditioning cycleturbine 65 is enough to pump about 50% of the cycle flow, and the powercycle compressor 62 compresses the remainder, along with the power cycleturbine flow. Thus, the power cycle in this arrangement providespneumatic power by evacuating the low pressure side of the conditioningcycle. The conditioning cycle air, compressed to atmospheric pressure bythe compressors 62, 66, is vented to ambient.

Because in the cooling mode the cycle is run at sub-atmosphericpressure, the Brayton power cycle must be run in a closed loop.Therefore the discharge air from the turbine 61, after passing throughthe recuperator 36, is cooled by the sink heat exchanger 38 beforereturning to the power cycle compressor inlet. In the cooling mode, noneof the power cycle air enters the house, and the cooling is provided bythe conditioning cycle portion only.

FIGS. 5 and 6 illustrate schematically an electrically driven heat pumpsystem in accordance with the invention which is essentially the same asthe systems depicted in FIGS. 1-3 except that an electric motor issubstituted for the primary drive which was supplied by a Brayton cycleturbine in the heat driven systems. Thus FIGS. 5 and 6 use correspondingreference numerals to designate corresponding elements which are commonto the arrangements of FIGS. 1-3. This electrically driven systemincludes a turbo-compressor 70 comprising turbine 72 and compressor 74as the conditioning cycle turbomachine. Mounted on the turbo-compressorshaft is an electric motor 76, shown for connection to electric mainsand controlled by a suitable control circuitry (not shown). The motor 76includes a heat exchange element 78 in the form of a coil carrying airfrom the compressor 74. A by-pass valve 79 is mounted in the outlet linefrom the compressor 74 and, for the heating mode operation as shown inFIG. 5, is in the blocked position.

As shown in FIG. 5, cold ambient air ducted from outside the house isfirst heated in the regenerative heat exchanger 24 to near thetemperature of the heated space and is then ducted through valve 28 tothe compressor 74. The air is then compressed and its temperature israised well above that required for the heated space and is ductedthrough the load heat exchanger 12 where it provides the heat for therecirculated air. It then returns through the regenerative heatexchanger 24, is cooled to near ambient temperature, and is thenexpanded across the turbine 72 to a temperature well below ambient andis exhausted through the valve 26. This expansion process provides aportion of the energy required to drive the compressor 74. The remainingenergy is provided by the electric motor 76. The air from the compressor74 passes through the loop 78, cooling the motor 76 and picking up themotor heat for further heating of the house circulation air in the loadheat exchanger 12.

In the cooling mode, depicted in FIG. 6, the electrically driven heatpump system operates to initially cool the warm ambient air in theregenerator 24. This air then flows to the turbine 72 where it isexpanded to sub-atmospheric pressure. The temperature decreases wellbelow the temperature of the conditioned space and this cooled air drawsheat from the circulation air in the load heat exchanger 12. Water isinjected at the inlet of the load heat exchanger 12, as alreadydescribed, for further cooling due to evaporation of the water. Asbefore, the expansion energy at the turbine 72 provides a portion of theenergy required for the compressor 74. The remainder of the necessaryenergy is provided by the electric motor 76. Cycle air from theregenerator 24 is directed to the compressor 74 where it is compressedback to ambient pressure and is exhausted through valve 26.

If desired, the system of FIGS. 5 and 6 may be modified along the linesshown and described for the system of FIG. 3 to divert a portion of therecirculation air through the cooling element associated with the motor76 so that the waste motor heat is transferred directly into therecirculation air.

By virtue of the various arrangements in accordance with the presentinvention as shown in the accompanying drawings and describedhereinabove, a particularly effective and efficient heat pump system forresidential use may be realized. Each of the various componentsincorporated in the systems are readily available, off-the-shelf items.For example, the recuperator (and other heat exchanger components, asdesired) may utilize structure corresponding to the formed plate typeheat exchanger of U.S. Pat. No. 4,073,340 of Kenneth O. Parker, assignedto the Assignee of this invention. The combustor may correspond to thatdescribed in the above-mentioned article by Friedman. The coefficient ofperformance (COP), as defined by Friedman, compares favorably with theCOP of existing systems, with which the systems of the present inventionare designed to compete. In one embodiment of the heat driven air cycleheat pump, the system is estimated to have a heating COP ofapproximately 1.6 on a 45° F. day (in the heating mode). It is worthnoting that as the ambient temperature falls below 45° F., this systemdoes not have a reduction in total heating capacity, as is common withconventional vapor compression equipment. In addition, the heating COPwill also not diminish to any great extent. Another important advantageof this system is the fact that, since the ambient air is heated in theregenerated heat exchanger, there is no frost problem commonlyassociated with vapor compression equipment. In the cooling mode, thesystem is capable of achieving a COP of 0.8, which is improved to avalue exceeding 1.0 through the utilization of the water spray techniqueas shown in FIG. 2.

Systems in accordance with the present invention, when compared withexisting installed gas furnaces and electrical air conditioning systemshave been estimated to have a favorable pay-out time, by virtue of theirimproved efficiency and reduced operating costs, of five to ten years.With economies to be realized from higher volume production, and at thepresently high and apparently increasing cost of fuel, the pay-out timefrom economy of operation should reduce substantially.

Although there have been described above specific arrangements of heatpump systems for residential use in accordance with the invention forthe purpose of illustrating the manner in which the invention may beused to advantage, it will be appreciated that the invention is notlimited thereto. Accordingly, any and all modifications, variations orequivalent arrangements which may occur to those skilled in the artshould be considered to be within the scope of the invention.

What is claimed is:
 1. The method of heating an enclosed spacecomprising the steps of:drawing in ambient air to a regenerator forheating by transferring heat from conditioned air from a load heatexchanger; directing the heated ambient air to the compressor element ofa turbo-compressor for conditioning by compressively heating therein;directing the heated conditioned air to the load heat exchanger;directing the conditioned air from the regenerator to the turbineelement of the turbo-compressor for developing power to assist indriving the compressor before exhausting the air from the turbine toambient; driving the compressor with a Brayton turbine mounted on acommon shaft and coupled to be driven by combustion heated gases from acombustor/heat exchanger; directing the expanded gases from the Braytonturbine to a recuperator for inlet air to the combustor/heat exchanger,thence to a sink heat exchanger for transferring waste heat to ambient,and thereafter to the inlet of the compressor for combination with theconditioned air from the regenerator; and directing a portion of the airfrom the compressor to the recuperator for inlet air to thecombustor/heat exchanger.
 2. The method of providing heated conditionedair to an enclosed space comprising the steps of:exchanging heat betweenconditioning air from a load heat exchanger and ambient air in aregenerative heat exchanger; directing heated ambient air to acompressor of a turbo-compressor to compress and further heat the air;directing the heated conditioning air through the load heat exchanger toheat the conditioned air to be provided to the enclosed space; directingconditioning air from the regenerative heat exchanger to the turbine ofthe turbo-compressor to expand the conditioning air therein; driving theturbo-compressor with a Brayton turbine receiving combustion gases froma combustor/heat exchanger; directing the Brayton turbine exhaust gasesto a recuperator to transfer heat to inlet air for the combustor/heatexchanger; directing the turbine exhaust gases from the recuperator to asink heat exchanger to transfer heat to the enclosed space; anddirecting exhaust gases from the sink heat exchanger to the compressorof the turbo-compressor for combination with the heated ambient air.